Identifying Key Spatiotemporal Regions of the Local Source of the Northern Yellow Sea Cold Water Mass

The Northern Yellow Sea Cold Water Mass (NYSCWM) is a distinctive hydrographic phenomenon in China’s coastal waters and is generally considered to originate from locally formed cold water during the previous winter. However, the specific wintertime period and local spatial range controlling its bottom-layer minimum temperature (BMT) remain unclear. This study utilizes August BMT data spanning 2003–2020, together with winter Multiscale Ultrahigh Resolution Sea Surface Temperature (MURSST) data. On this basis, K-means clustering is applied to identify the key spatiotemporal regions linked to BMT variability. Results show that the BMT of the NYSCWM exhibits a significant warming trend of about 0.0533 °C yr−1 and a pronounced quasi-3-year oscillation. The strongest correlation (CC = 0.8396) between BMT and winter SST occurs in the central Northern Yellow Sea (NYS) during the second half of February, exceeding that in other regions. This area acts as a key spatiotemporal region, located between colder western waters and warmer southern sectors, and maintains persistently low temperatures during this period. A regression model based on SST in this key spatiotemporal region reproduces observed BMT with a correlation coefficient of 0.9146 and enables prediction six months in advance. These results refine the identification of key spatiotemporal regions and improve our understanding of NYSCWM formation and evolution.